The combination use of an industrial robot and machine tool, particularly an automatic machine tool such as an automatic lathe, is a technique widely employed to save labor and improve processing efficiency. Continuous unattended operation of an automatic lathe, for instance, is attained by having an industrial robot mount a work on the chuck of the automatic lathe, remove the work from the chuck after machining, return the machined work to the work table, then repeat the same mounting and removing operation. In such a machining operation, a double-hand type robot hand is often employed. The double-hand type robot hand is provided with right and left gripping units each adapted to perform individual work gripping operations. The right and left gripping units alternately grip a blank and a machined work so that the work replacing operation is attained sequentially, whereby the idle time of the machine tool is reduced to the minimum possible. In the operation of an industrial robot employing such a double-hand type robot hand, the industrial robot operates in accordance with commands provided by a robot control system to bring the right and left gripping units to positions opposite the chuck of a machine tool, such as an automatic lathe, by turning the wrist unit carrying the robot hand and performs work gripping and work replacing works. However, the right and left gripping units of the robot hand cannot be brought to the appropriate positions merely by turning the wrist unit 180.degree. since the work not yet machined and the machined work differ from each other in size and shape. This inconvenience may be eliminated by the measure of adapting the robot work command, which is taught beforehand to the robot control system, to the required robot work. It would, however, be extremely convenient if this inconvenience could be eliminated simply through the control of the robot hand.